(a) Field
The present invention relates to an apparatus for controlling a state of charge of a hybrid vehicle and a method using the same, and more particularly, to controlling a state of charge (SOC) of a hybrid vehicle by determining a virtual center SOC to control a SOC of a battery.
(b) Description of the Related Art
Hybrid electric vehicles may have various structures in which two or more kinds of power sources including an engine and a motor are used. A transmission mounted electric device (TMED) type of power train in which the motor, a transmission, and a drive shaft are connected in series is applied to hybrid electric vehicles.
In addition, an engine clutch is provided between an engine and a motor, and hybrid electric vehicles may be driven in an electric vehicle (EV) mode or a hybrid electric vehicle (HEV) mode depending on whether the engine clutch is engaged or not.
The EV mode refers to a mode in which the vehicle is driven only by driving torque of the motor, while the HEV mode refers to a mode in which the vehicle is driven by driving torque of the motor and the engine. Accordingly, when the hybrid electric vehicle is driven, the engine may be turned on or turned off.
When a high voltage battery is applied to the TMED type of power train, the engine may be turned off in the EV mode. Basically, the engine is controlled to be turned on or off in accordance with an optimal operating point of the engine. For example, in order to control the engine to be turned on or off, the hybrid vehicle has different SOC references by dividing a driving state according to an expressway, a national highway, and a downtown area.
That is, the hybrid vehicle is operated primarily in the HEV mode to charge a battery by controlling the engine to be turned on when driven on the expressway or the national highway, thus having high charging efficiency. In addition, the hybrid vehicle is operated primarily in the EV mode to discharge the battery by controlling the engine to be turned off when driven in the downtown area, thus having low charging efficiency.
Depending on the driving state of the hybrid vehicle, engine operation controls the SOC to be changed. However, as the engine operation may vary, it is difficult to instantly reflect the driving state of the hybrid vehicle. Accordingly, many difficulties are encountered in maintaining the SOC at a predetermined level.
This is because the SOC is not flexibly changed in accordance with a downtown section having low charging efficiency, a medium and high speed section having high charging efficiency, and an ultra-high speed section having low charging efficiency, but it is simply set to normal, charge, and discharge sections.
Accordingly, fuel efficiency of the engine may deteriorate due to entering an idle charge state, entering a full load state, and frequent departures from a normal SOC section.
The above information disclosed in this Background section is only to enhance the understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.